In this study we have investigated the export and fate of two extracellular enzymes produced by S. salivarius. Glucosyltransferase (GT) export was markedly affected by the physical state (fluidity) of the cytoplasmic membrane. When the membrane lipids were enriched with oleic acid (48% of the total fatty acids) by growing the organism in medium containing Tween 80, the differential rate of appearance of extracellular GT was very rapid compared to that observed with cells whole membrane lipids had a much lower content of oleate (27%). This effect appears to be specific for oleate and not just a function of a general increase in the unsaturated:saturated (U:S) membrane fatty acid ratio. Growing cells at 30C in the absence of Tween 80 resulted in a U:S fatty acid ratio identical to that observed when the organism was grown at 37C in the presence of Tween 80. In this case, however, the increase in the U:S ratio was due to an enrichment of the membrane lipids with cis-vaccenate rather than oleate and the organism was unable to export GT. Another aspect of this study deals with the mechanism of inactivation of a cell-associated fructosyltransferase (FT) that occurs under certain physiological conditions. Inactivation of FT occurs by an initial redox reaction that serves to "mark" the enzyme. The modified FT is thus rendered a substrate for proteolysis.